Cyclic Array of Twisted Donor-Acceptor Conjugates Leading to Deep Blue Thermally Activated Delayed Fluorescence.

Achieving thermally activated delayed fluorescence (TADF) from covalently assembled multiple donor-acceptor (D-A) units is challenging due to complex design issues. Here, we use a cyclic multiple donor-acceptor (CPCQ) design approach that includes four nonconjugated TADF active D-A units. Spectroscopic analysis revealed that CPCQ emits deep blue TADF (430 nm) with (a) a high photoluminescence quantum yield (PLQY, 78-80%), (b) a high reverse intersystem crossing rate (k = 2.68 × 10 s), and (c) a low singlet-triplet energy gap (ΔE = 0.13 eV) compared to the parent D-A conjugate. The CPCQ blend (1.0 wt%) also shows blue TADF with a PLQY of 63%. Quantum studies reveal that this strategy enables through-space charge transfer that lowers ΔE and boosts local triplet density─missing in PCQ─driving faster, more efficient RISC in CPCQ. This finding holds great promise for new directions for designing energy-efficient TADF emitters.